Sometimes the name of the microorganisms and the microbial diseases are derived from the place of the first isolation of the organism or occurrence of the disease. These names may create confusion later because the organism or disease initially confined in a particular location, now may be prevalent in various parts of the world. In this blog post, I have compiled a list of some such diseases and their etiological agents.
California Encephalitis Virus
California encephalitis virus, a member of the bunyavirus family, was first isolated from mosquitoes in California in 1952, but its name is something of a misnomer because the most human disease occurs in the north-central states of USA. The strain of the California Encephalitis virus that causes encephalitis most frequently is called La Crosse (for the city of Wisconsin where it was first isolated).
La Crosse virus is the most common arboviral cause of encephalitis in the United States of America. It is transmitted by the mosquito Aedes.
Colorado Tick Fever Virus (CTF)
Colorado tick fever is a reovirus transmitted by the wood tick among the small rodents eg, Chipmunks and Squirrels, of the Rocky Mountains. There are approximately 100-300 cases per year in the United States of America.
This disease occurs primarily in people hiking or camping in the Rocky Mountains and is characterized by fever, headache, retro-orbital pain, and severe myalgia. Diagnosis is done by virus isolation (from blood) or by detecting the rise in antibody titer. No antiviral therapy or vaccine is available. Prevention involves wearing protective clothing and inspecting the skin for ticks.
Eastern Equine Encephalitis Virus
It is a member of the togavirus family. It causes encephalitis along the east coast of the United States of America. Encephalitis is severe but uncommon. This virus is transmitted to humans by mosquitoes from small wild birds, such as sparrows. There is no antiviral therapy and nonvaccine for humans.
Ebola virus a member of the filovirus family is named for the river in Zaire that was the site of the outbreak of hemorrhagic fever in 1976. The mortality rate associated with the Ebola virus is nearly 100%. Ebola virus causes shock, gastrointestinal bleeding disseminated intravascular coagulation. Severe thrombocytopenia causes hemorrhages.
Most of the cases arise from secondary transmission from contact with the patient’s blood or secretions. The natural host of this virus is unknown. Diagnosis of Ebola viral disease is made by isolating the virus or by detecting the rise in antibody titer.
Human African trypanosomiasis (HAT), or African sleeping sickness
Human African trypanosomiasis (HAT), or sleeping sickness, is caused by a protozoan parasite; Trypanosoma brucei.
This vector-borne parasitic disease is transmitted by the bite of infected tsetse flies of the genus Glossina. Human African trypanosomiasis takes 2 forms; Trypanosoma brucei gambiense is found in 24 countries in west and central Africa and Trypanosoma brucei rhodesiense are found in 13 countries in eastern and southern Africa.
Japanese Encephalitis Virus
It is the most common cause of epidemic encephalitis. The disease is most prevalent in South East Asia. Japanese Encephalitis virus is a member of the flavivirus family. It is transmitted to humans by certain species of Culex mosquitoes endemic to Asian rice fields. Disease diagnosis can be done by isolating the virus, detecting IgM antibodies in serum or spinal fluid, or by staining brain tissue with fluorescent antibodies. There is no antiviral therapy.
Lassa Fever Virus
This virus was first seen in Lassa town of Nigeria in 1969. Lassa fever virus is a member of the arenavirus family and causes Lassa fever, an animal-borne, acute viral illness.
It causes a severe, often fatal hemorrhagic fever, and death occurs by vascular collapse. The virus is transmitted to humans by contamination of food or water contaminated with animal urine. A small rodent called Mastomys is the natural host for the Lassa fever virus. Ribavirin if given early reduces the mortality rate. No vaccine is available.
It is a member of the filovirus family. It causes hemorrhagic fever with a mortality rate of nearly 100%. Marburg virus was first recognized as a cause of human disease in 1967 in Marburg, Germany. Natural reservoir of the Marburg virus is still unknown. In 2005, Marburg virus outbreaks killed hundreds of people in Angola. Isolation of virus or detection in rise in antibody titre is used as diagnostic tools. No antiviral therapy and vaccine are available.
Rift Valley Fever
Rift Valley fever (RVF) is a viral disease of domestic animals in Sub-Saharan Africa. People get Rift Valley fever through contact with blood, body fluids, or tissues of infected animals or through bites from infected mosquitoes.
As the symptoms of this disease are non-specific, diagnosis is made by virus isolation in cell culture and reverse transcriptase-polymerase chain reaction or RT-PCR.
Onchocerciasis, also known as river blindness is caused by the worm Onchocerca volvulus. It is spread to humans and animals through the bite of a type of black fly of the genus Simulium.
Rocky Mountain Spotted Fever
Rocky Mountain spotted fever (RMSF) is one of the deadliest tick-borne bacterial diseases in the Americas. RMSF cases occur throughout the United States but are most commonly reported from North Carolina, Tennessee, Missouri, Arkansas, and Oklahoma. The etiological agent of RMSF is Rickettsia rickettsii, an intracellular bacteria.
St. Louis Encephalitis Virus
St. Louis encephalitis virus is found in the southern, central, and western states and causes 10-30 cases of encephalitis per year in the United States. St. Louis encephalitis virus is transmitted by several species of Culex mosquitoes. Small wild birds esp English sparrows are the reservoir and humans are the dead-end hosts. In contrast to the eastern equine encephalitis virus and western equine encephalitis virus which are predominantly rural, St. Louis encephalitis virus occurs in urban areas (because of the preference of these mosquitoes to breed in stagnant water)
Western Equine Encephalitis Virus
It causes less severe illness and 5-20 cases of western equine encephalitis virus occur every year in the USA with a mortality rate of 20%. This virus is transmitted primarily by Culex mosquitoes among a wild-bird population of the western states, especially in areas with irrigated farmland. No antiviral therapy for humans is available. Diagnosis is made by isolating the virus or observing a rise in antibody titer.
West Nile Virus (WNV)
West Nile virus is a flavivirus that is classified in the same antigenic group as St. Louis encephalitis virus. It is endemic in Africa but has caused encephalitis in areas of Europe and Asia as well. Wild animals are the main reservoirs of this virus, which is transmitted mainly by the infected Culex mosquitoes.